Implement CAN signal labels

[nspo]

Implement reading/writing of labels in KCD files
Implement optional matching of labels when unpacking (is this the best way?)
Unit tests
Change ifconfig to ip command

[nspo]

I just found out that sometimes there are some signals with labels that should probably be matched like flags:

<LabelSet>
    <Label value="0" name="no_error"/>
    <Label value="1" name="error1"/>
    <Label value="2" name="error2"/>
    <Label value="4" name="error3"/>
    <Label value="8" name="error4"/>
</LabelSet>

I'm not sure whether it would be wise to implement different kinds of label matching, leave it like it's in the PR or just leave every kind of matching to the user.